Lighting device for a discharge lamp

ABSTRACT

In a lighting device for a discharge lamp including a ballast inserted between an AC power source and a discharge lamp the ratio ZC/ZL of the capacitive impedance ZC to the inductive impedance ZL of the ballast is in the range of 1.9-2.8; the ratio VL/VS of the nominal lamp voltage VL of a discharge lamp to the unloaded voltage VS of a power source is in the range of 0.7-1.1; and when VL/VS is in the range of 1.0-1.1, the ratio VL/VS is so determined as to satisfy the equation:

United States Patent 11 1 Nomura et al..

[ Dec. 25, 1973 LIGHTING DEVICE FOR A DISCHARGE LAMP Inventors: Osamu Nomura, Yokohama,

Kanichi Yajima, Tokyo, both of Japan Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan Filed: Nov. 28, 1972 Appl. No.: 310,131

Assignee:

Foreign Application Priority Data Aug. 25, 1972 Japan 47/85030 US. Cl. 315/105, 315/244 Int. Cl. 11051) 39/00 Field of Search 315/244, 105, 94

References Cited UNITED STATES PATENTS 9/1941 Thayer 315/105 X 2,302,213 11/1942 Hall,.lr. ..315/105X Primary Examiner-Nathan Kaufman Attorney-Robert D. Flynn et al.

1 Claim, 5 Drawing Figures PATENTED DEEZS I975 FIG. 2

FIG.

FIG. 3

FIG. 4A

FIG. 4B

LIGHTING DEVICE FOR A DISCHARGE LAMP BACKGROUND OF THE INVENTION The present invention relates to a lighting device for a discharge lamp and particularly to a lighting device in which a ballast has the optimum requirement for being light in weight and compact.

Generally, a lighting device for a discharge lamp must have the functions of easily starting a discharge lamp, stably maintaining the lighting of the discharge lamp and holding down the output variation of the discharge lamp even if a power source voltage is varied. For this reason a ballast'is so constructed that in order to light a discharge lamp the ratio V,/V of the unloaded voltage V of a power source to the nominal lamp voltage V, is a relatively small value of 0.450.5.

However, the smaller. the ratio V,,/V the larger the ballast with the attendant increase in weight. As set out above, in an attempt to improve the variation rate of a lamp voltage a phase advance type lighting device is used. In this case, if a suitable balance between the inductance L and the capacitance C of the ballast is not taken, a flicker occurs and parts of ballast are increased in size and it is disadvantageous from the practical point of view.

Accordingly, the object of the present invention is to provide a lighting device for a discharge lamp including a ballast capable of being maintained at optimum condition without involving any flickering or fading out and having the optimum requirement of being lit in weight and compact.

SUMMARY OF THE INVENTION The lighting device according to the present invention including a discharge lamp is operated by an AC power source and a ballast is inserted between the AC power source and the discharge lamp. The ratio Z /Z of the capacitive impedance 2,; to the inductive impedance 2, of the ballast is in the range of 1.9-2.8; the ratio V /V of the nominal lamp voltage V of the discharge lamp and the unloaded voltage V of the power source is in the range of 0.7-1.1; and when the ratio is in the range of 1.0-1.1, Z Z, V and V are defined to satisfy the following equation:

1. V /Vg 7.1

When the above-mentioned relation exists between Z and Z,, of the ballast and unloaded AC power source voltage V,- and nominallamp voltage V,,, not only a very stable lighting state of the discharge lamp is maintained, but also a compact, light weight ballast results.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram showing one embodiment according to the present invention;

FIG. 2 is a schematicdiagram showing another embodiment according to the present invention;

FIG; 3 is an explanatory diagram of the characteristics of the device according to the present invention; and

FIG. 4 shows the waveform of a voltage applied to the discharge lamp of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 a discharge lamp 2 is connected, through a ballast 3, between the terminals of an AC voltage source I. The ballast consists of an inductive impedance element, for example, a choke coil 4 and a capacitive impedance element, for example, a condenser 15. The inductive impedance and capacitive impedance are denoted as 2, and Z respectively, and the unloaded voltage of the power source 1 and the nominal lamp voltage of the discharge lamp are denoted as V and V respectively. Between the terminals of the power source 1 there is connected a pulse generating circuit 6 driven by the voltage of the power source. An output pulse from the pulse generating circuit is fed to a tap 7 of the choke coil 4.

When the switch (not shown) of the power source is thrown in, an output pulse from the pulse generating circuit 6 is applied to the tap 7. The voltage of the output pulse is boosted by the choke coil 4 and a hightension pulse is generated across the choke coil. The high-tension pulse is applied, in a manner to be overlapped by an AC voltage from the power source, between the electrodes of a discharge lamp 2 to light the discharge lamp. In this circuit arrangement, experiments wer conducted by varying not only the ratio Z /Z of the capacitive impedance 2 to the inductive impedance 2,, of the ballast, but also the ratio V,jV of the nominal lamp voltage V of the discharge lamp to the unloaded voltage V of the power source and it was observed that the area in which no flickering and fading out occur is a rectangular area defined by lines a, h, c and d as shown in FIG. 3. From this are an optimal data for permitting the ballast to be smaller in size and light in weight can be obtained.

I In FIG. 3 the abscissa and the ordinate are represented as the ratio V /V (nominal lamp voltage/unloaded voltage of the power source) and the ratio Z /Z (capacitive impedance/inductive impedance of the ballast), respectively. Let us now explain the'reason why the area outside the rectangular area as defined by a, b, c and d is unfit for a lighting device. At the area of Y Y fias ut s9 sl lqsps t q tanua ue Z /Z At the area of 1.0 V /V 1.1 the area in which an excellent lighting state is continued is intermingled with the area in which fading out occurs. This is dependent upon the ratio Z ;/Z That is, at the area of V /V l the situation in which Z /Z 1.9 is different in refiring voltage from the situation in which Z /Z =2.8. In this case, no fading out occurs with the in-- crease in the value Z/Z flhTlG. 4A th e refiring voltage waveform (peak value V is shown at the area of VL/V =1.0 and ZCIZL=Q and in FIG 4B the refi ring voltage waveform (peak value V is indicated at the area of V /V 1.0 and Z /Z 1.9. These waveforms are different from each other and the relation V V is obtained. In other words, in the range of 1.0-1.1 of V'JV fading out tends to occur at VJV 1.0 when ZC/Z,,=l.9, and fading out occurs at VL/VS 1.1 when Z /Z When the ratio Z Z L is in the range of 1.9-2.8 fading out tends to occur at that point From this it will be understood that a lighting device having a relation of V /V to 2 /2,, corresponding to that right side area as defined by the line a is infeasible from a practical view point.

In that upper area as defined by the line c a value of 2 /2,, is greater which means that a capacitive component Z is increased. Therefore, a rest period is involved at the lamp current and flickering is caused due to this rest period. In the area of Z /Z 2.8 flickering takes place irrespective of any value V /V and it is undesirable from the practical point of view. In an attempt to prevent flickering at a lower temperature C) it is some time desirable that Z /Z be below 2.6.

In those areas as defined by V, /V 0.7 and Z /Z 1.9, that is, the left side area defined by the line b and the lower side area defined by the line d, the inductive impedance Z and capacitive impedance Z of the ballast become greater. In this case, a ballast will be largesized and it is therefore undesirable. To explain in more detail, in those areas the inductive impedance Z of the ballast becomes greater than that of a phase lagging type ballast having inductive impedance only and, in addition, a lamp voltage varied with a power source presents no difference from the case in which a phaselagging type ballast is used.

Let us now numerically explain the discharge lamp lighting device according to the present invention. Use was made of alightj g device fora llOW high output fluorescent lamp having a power source voltage V of 200V, a frequency of 50 Hz, a ballast inductance L of 600mH, a ballast capacity C of 7.3}LF and a nominal voltage V of 159V. In this case the ratio of the capacitive impedance Z to the inductive impedance Z is given as follows:

The ratio of the nominal voltage V,, to the unloaded voltage of the power source is expressed below.

Vl./Vs 159/200 0.795

This lighting device falls within the area as specified in FIG. 3, that is, on a point P and exhibits an excellent lighting state.

Then, use was made of a lighting device for a 220W high output fluorescent lamp having a power source voltage of 200V, a frequency of SOI-Iz, a ballast inductance L of 360mI-I, a ballast capacitance C of 12.6[LF and a nominal lamp voltage V of 173V. In this case the ratio Z /Z is expressed as follows:

The ratio V /V is given below:

v,./vS= 173/200 3x8 5 That is, this lighting device falls on a point 0 within the area as defined in FIG. 3 and exhibits an excellent lighting state.

As explained above, a lighting device capable of maintaining an excellent lighting state and having a small-sized, light weight ballast is obtained by restricting the relation of Z /Z to V /V specifically to the area as defined by lines a, b, c and d.

The pulse generating circuit 6 as shown in FIG. 1 can be omitted in a case where no pulse is necessary when a discharge lamp is started.

In FIG. 2 there is shown another embodiment according to the present invention in which a leakage transformer 8 is used as an inductive impedance element of a ballast 3. In this case, since the voltage of a power source la is boosted by the secondary winding of the leakage transformer, the above-mentioned voltage V means a voltage applied between the electrodes of a discharge lamp before the starting of the discharge lamp. In this embodiment the operational function is substantially the same as the embodiment of FIG. 1 and any further explanation is therefore omitted.

What we claim is:

l. A lighting device for a discharge lamp including a discharge lamp fed from an AC power source and a ballast arranged between the discharge lamp and the AC power source and including a capacitive impedance Z and an inductive impedance Z,,, in which a ratio Z /Z of the capacitive impedance Z to the inductive impedance is in the range of 1.9-2.8; a ratio V /V of a nominal lamp voltage V of the discharge lamp to an unloaded voltage V of the power source is in the range of 0.7-1.1; and when the ratio V /V is in the range of 1.0-1.1 it satisfies the equation: 

1. A lighting device for a discharge lamp including a discharge lamp fed from an AC power source and a ballast arranged between the discharge lamp and the AC power source and including a capacitive impedance ZC and an inductive impedance ZL, in which a ratio ZC/ZL of the capacitive impedance ZC to the inductive impedance is in the range of 1.9-2.8; a ratio VL/VS of a nominal lamp voltage VL of the discharge lamp to an unloaded voltage VS of the power source is in the range of 0.7-1.1; and when the ratio VL/VS is in the range of 1.0-1.1 it satisfies the equation: ZC/ZL > OR = 9VL/VS-7.1. 